The present invention relates to apparatus and methods for sealing between the inner retainer segment and an inner platform rail of a nozzle segment in a gas turbine and particularly relates to seal assemblies for increasing sealing and turbine engine efficiencies by reducing leakage between a high pressure region for supplying cooling air to the turbine nozzles and a forward rotor rim cavity including the hot gas path outboard of the rim cavity.
In gas turbines, hot gases of combustion flow from combustors through first stage nozzles and buckets and through follow-on stages. The first stage nozzles typically include an annular array or assemblage of cast nozzle segments each containing one or more nozzle stator vanes per segment. Each nozzle segment also includes inner and outer platforms or bands spaced radially one from the other. Upon assembly of the nozzle segments into the turbine, the stator vanes are circumferentially spaced from one another to form an annular array thereof between annular inner and outer platforms. The outer and inner platforms are secured to an outer casing and an inner support ring respectively. The inner support ring is typically split at the horizontal mid-line of the turbine and is engaged by radially inwardly dependent inner platform rails supporting the nozzle segments against aft axial movement.
The annular array of nozzle segments are sealed one to the other along adjoining circumferential edges by side seals. The side seals seal between the high pressure region radially inwardly of the inner platform, i.e., a region of compressor discharge air at high pressure, and the rotor rim cavity as well as the hot gases of combustion in the hot gas flow path which are at a lower pressure. In a typical gas turbine, the greatest pressure drop in the turbine occurs between this first stage nozzle cooling air supply plenum and the forward rotor rim cavity including the hot gas path outboard of the rim cavity. A seal is also typically provided at the sliding interface between each nozzle rail and the inner support ring to contain this pressure differential. A chordal land seal is conventionally used to seal between these components and comprises a narrow raised land of material integral to the aft face of each rail. The ends of the seal lands between adjacent nozzles align radially forming a full annular land bearing on the forward face of the support ring. The sealing efficiency of nozzle chordal land seals is limited, however, by 1) an uneven sealing load along the seal land length caused by circumferential torque generated by the nozzle; 2) lack of flatness of the seal lands and support ring caused by thermal distortion of the nozzle and support ring as well as seal surface variations resulting from manufacturing limitations; and 3) a lack of smooth surface finish on the chordal seal lands and support ring resulting from surface galling and corrosion during operation.
A number of different types of sealing systems have been proposed to improve the sealing efficiency and hence turbine efficiency between the region of high pressure compressor discharge air and the rotor rim cavity. For example, U.S. Pat. Nos. 6,641,144; 6,572,331; 6,637,753; and 6,637,751 disclose various seals supplemental to the chordal seals for this region of the turbine.
In accordance with a preferred aspect of the present invention, there is provided a seal assembly which affords additional reduction in cooling air leakage across the nozzle chordal land seal thereby improving overall turbine efficiency. More particularly, a barrier to the high pressure compressor discharge air is created between the inner retainer segments and the forward face of the nozzle inner rail. Preferably finger seal assemblies form a full annulus and seal along the full circumference of the forward face of the nozzle inner rails. When combined with the inter-segment seals at the first stage inner rail, i.e., the chordal seals, the finger seals form an intermediate pressure plenum upstream of the nozzle aft chordal land seals and which seals in series dramatically increase sealing efficiency and reduce leakage.
In a preferred embodiment according to the present invention, there is provided a turbine comprising a turbine nozzle segment having at least one stator vane and including an inner platform rail; a turbine nozzle inner support ring in part in axial registration with the rail on one side thereof; an inner retainer segment secured to the inner support ring and in part in axially spaced registration relative to the rail on an axial side of the rail opposite from the support ring; and a seal assembly extending between the inner retainer segment and the rail, the seal assembly including a plurality of seal fingers secured to the inner retainer segment and in engagement with the rail.
In a further preferred embodiment according to the present invention, there is provided a turbine comprising a plurality of nozzle segments arranged about a turbine axis with each segment having at least one stator vane and an inner platform carrying an inner platform rail; inner nozzle support rings in part in spaced axial registration with the rails and on one axial side of the rails; a plurality of inner retainer segments secured to the inner supporting rings and in part in axial spaced registration relative to the rails on an axial side of the rails from the support rings; and a seal assembly between the inner retainer segments and the rails, the seal assembly including a plurality of circumferentially spaced inner retainer seals each including a plurality of circumferentially spaced seal fingers for sealing engagement with the rails.
In still another preferred embodiment in accordance with the present invention, there is provided a method of installing a seal assembly in a turbine having a plurality of nozzle segments arranged about a turbine axis with each segment having at least one stator vane and an inner platform carrying an inner platform rail and inner nozzle support rings in part in spaced axial registration with the rails and on one axial side of the rails for sealing between high and low pressure regions on opposite sides of the rails, comprising the steps of providing a plurality of inner retainer segments secured to the inner supporting rings and in part in axial spaced registration relative to the rails on an axial side of the rails opposite from the support rings; securing a plurality of circumferentially spaced inner retainer seals each including a plurality of circumferentially spaced seal fingers to the inner retainer segments; and securing the inner retainer segments with the seals secured thereto to the support rings with the seals extending from the segments into sealing engagement with the rails on the axially opposite sides thereof from the support rings.